Method and apparatus for charging batteries with energy storage

ABSTRACT

According to a first aspect of the invention a battery charger and method of charging a battery includes an input circuit that receive an ac input having a period of T seconds and provides a dc signal. A converter receives the first dc signal and provides a converter output across a dc bus having a peak voltage of V volts. An output circuit receives the dc signal and provides a battery charging signal having a power of P watts. A controller, controls the converter to provide power factor correction. A bus capacitor is connected across the dc bus and has a capacitance of at least (3PT)/(V 2 ) farads, or a capacitance to store sufficient energy to maintain the available output power signal through the duration of mechanical transient. The capacitance may be at least (4PT)/(V 2 ), (5PT)/(V 2 ), or (5.5PT)/(V 2 ). Multiple output circuits may be provided, connected either one at a time, or a number at a time.

FIELD OF THE INVENTION

The present invention relates generally to the art of battery charging.More specifically, it relates to battery charging using versatilecircuitry that can preferably be used with a generator or with “dirty”power.

BACKGROUND OF THE INVENTION

There are a large number of rechargeable batteries having a wide varietyof voltages and charging schedules. (Charging schedule, as used herein,is the manner in which the charging is performed for a given battery.For example, one charging schedule might call for a limited amount ofcurrent initially, and then a greater current when the battery voltagecrosses a threshold, followed by a trickle charge after the batteryvoltage crosses a second threshold.) It is typical that a charger bedesigned for a single battery type, and have a single output voltage andcharging schedule. Of course, dedicated battery chargers are notversatile, and can require a facility to have a number of chargers.

Other chargers are not dedicated, but are “dumb” chargers that apply aconstant voltage output with the charging current being controlled bythe load, not the charger. These chargers might work for any battery ofa given voltage, but do not optimally charge batteries. Thus, if suchchargers are used to charge several batteries simultaneously, theycannot provide a unique charging current or voltage for each battery.Rather, a single charging schedule is used for all batteries beingcharged. This also diminishes the usefulness of chargers.

Some battery chargers are inefficient because they have a poor powerfactor. This causes increased costs when power is utility power, and canlessen the charging capacity, particularly when using generator power.The use of generator power can cause another problem—generators oftenprovide “dirty” power, i.e., power that is not perfectly sinusoidal, ornot of a constant value. Dirty power can result in improper charging.

Prior art battery chargers are often design for a single input voltageand frequency. While this might be sufficient for consumer batterychargers, some applications, such as industrial battery charging, orautomotive charging, might be used at different locations where theinput power is not the same.

Rechargeable batteries have a finite life, in that their ability to becharged diminishes over time. Often, a user finds the battery is nolonger chargeable by charging it, then using it, and having the batterybecome discharged in a short period of time.

Accordingly, a battery charger that is versatile enough to chargedifferent types of batteries, or to simultaneously charge batteries withdifferent outputs, is desirable. A modular design, where output circuitsfor particular batteries can be switched in and out by the user, is onemanner to allow different charging schedules. Also, a single outputmodule could be used for any battery type, where the user selects thebattery type, or the charger senses the battery type. Preferably, such acharger will provide power factor correction, and be able to receive awide range of inputs. Also, it will preferably be able to receive dirtypower, and still charge a battery. A charger that provides the user awarning when a battery is defective is also desirable.

SUMMARY OF THE PRESENT INVENTION

According to a first aspect of the invention a method and apparatus forcharging a battery includes an input circuit that receives an ac inputhaving a period of T seconds and provides a dc signal. A converterreceives the dc signal and provides a converter output across a dc bushaving a peak voltage of V volts. An output circuit receives the dcsignal and provides a battery charging signal having a power of P watts.A controller controls the converter to provide power factor correction.A bus capacitor is connected across the dc bus and has a capacitance ofat least (3PT)/(V²) farads.

According to a second aspect of the invention a method and apparatus forcharging a battery includes an input circuit that receives an ac inputhaving a period of T seconds and provides a dc signal. A converterreceives the dc signal and provides a converter output across a dc bushaving a peak voltage of V volts. An output circuit receives the dcsignal and provides a battery charging signal having a power of P watts.A controller controls the converter to provide power factor correction.A bus capacitor is connected across the dc bus and has a capacitance tostore sufficient energy to maintain the available output power signalthrough the duration of mechanical transients.

According to a third aspect of the invention a method and apparatus forcharging a battery includes an input circuit that receives an ac inputhaving a period of T seconds and provides a dc signal. A converterreceives the dc signal and provides a converter output across a dc bushaving a peak voltage of V volts. A plurality of user-removable outputcircuit can be connected, one at a time, to receive the dc signal andprovide a battery charging signals having a maximum power of P watts. Acontroller controls the converter to factor correction. A bus capacitoris connected across the dc bus and has a capacitance of at least(3PT)/(V²) farads.

According to a fourth aspect of the invention a method and apparatus forcharging a battery includes an input circuit that receives an ac inputhaving a period of T seconds and provides a dc signal. A converterreceives the dc signal and provides a converter output across a dc bushaving a peak voltage of V volts. A plurality of user-removable outputcircuit are connected to receive the dc signal and provide batterycharging signals having a combined power of P watts. A controllercontrols the converter to provide power factor correction. A buscapacitor is connected across the dc bus and has a capacitance of atleast (3PT)/(V²) farads.

The capacitance is at least (4PT)/(V²), (5PT)/(V²), and (5.5PT)/(V²) invarious embodiments.

The input stage includes an input rectifier that receives the ac inputsignal in another embodiment.

The battery includes a second output circuit, and the output circuit andthe second output circuit are connected at the same time, or mutuallyexclusively connected in various embodiments.

The converter is one of a buck converter, boost converter, buck-boostconvert and a combined rectifier-boost converter and the output circuitincludes a switched transformer in other embodiments.

Other principal features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a battery charger in accordance with thepreferred embodiment;

FIG. 2 is a circuit diagram of a preregulator in accordance with thepreferred embodiment;

FIG. 3 is a circuit diagram of an alternative preregulator in accordancewith the preferred embodiment;

FIG. 4 is a circuit diagram of an alternative preregulator in accordancewith the preferred embodiment;

FIG. 5 is a circuit diagram of an output circuit in accordance with thepreferred embodiment;

FIG. 6 is a circuit diagram of an output circuit in accordance with thepreferred embodiment;

Before explaining at least one embodiment of the invention in detail itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting. Like referencenumerals are used to indicate like components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention will be illustrated with reference to aparticular battery charger and particular circuitry, it should beunderstood at the outset that the invention may also be implemented withother circuitry, software and arrangements.

Generally, the invention is implemented by a battery charger thatreceives an input, such as an ac input, and provides a dc chargingoutput. Preferably, the battery charger may receive any input over arange of inputs without being reconfigured (i.e., re-linked orre-wired), and may be capable of receiving “dirty” power, such as thatfrom a generator. Also, the battery charger preferably includes anoutput stage that can either provide a number of voltages for chargingdifferent batteries, any voltage, or be designed for a single voltage.There can be a plurality of user-removable output stages. When theoutput circuits provides a single voltage, or a narrow range of voltagesfor charging one battery voltage, it is said to be designed for aparticular battery voltage. In one embodiment a number of output stagesare provided, each for charging one battery, wherein the batteries areof the same type or of different types.

When the output circuit is capable of charging different battery types,the user can set the battery type or voltage, or the charger can includea sensor. The sensor could be wired (i.e., connected to the battery andeither sense an ID signal, or sense the voltage of the battery), orwireless, such as an RFID sensor to sense an RFID tag on a battery. Thecharger preferably includes a controller that causes the output tofollow a charging schedule based on the battery type and/or voltage.

Another feature the charger preferably has is a “bad” battery detector,wherein the controller senses that a battery is not properly charging.The user is notified of the bad or defective battery. Anotheralternative provides a polarity detector to prevent damage to thebattery and/or charger if the battery is connected with the wrongpolarity.

The power provided for battery charging is not always ideal utilitypower, but might be “dirty” generator power. The present invention canprovide a battery charger that is capable of running off a generatorsource (as well as a utility source). A capacitor or other energystorage device delivers energy to a dc bus in such a way as to reducethe impact of dirty power on the charging circuit and allows forcharging during heavy loading of the generator source.

One advantage of the preferred embodiment is that it will operate usinga wide range of input powers, and thus is well-suited for applicationsor users that use the charger in multiple locations. Various embodimentsprovide for an input range of at least a factor of 2, at least twoutility voltages (115-230V, or 100-256V e.g.), 120V to 525V, or 100V to633V. The preferred embodiment is relatively lightweight, adding to thecharger]s portability. Additionally, the power circuit does not need tobe re-linked or reconfigured by the user for different powers, thusthere is less of a need to open the housing.

The details of the preferred embodiment will be provided below, but theygenerally include a rectifier, followed by a boost converter or abuck-boost converter, followed by a dc-dc converter, such as a pulsewidth or frequency modulated inverter or forward converter. A controllercontrols the boost converter to provide a dc bus having a desiredmagnitude, regardless of the magnitude and frequency of the input(within ranges), and to actively power factor correct the input. Thecontroller also controls the dc-dc converter using feedback of thebattery charging signal. Battery charging signal, as used herein,includes the signal used to charge the battery. For example, thecharging current is controlled using a current feedback loop. A voltagefeedback loop may be used to stop the charging process, or to change toa trickle charging mode. Controller 110 may use functions of the currentand/or voltage feedback and/or temperature feedback, such as power,energy, and integrals and derivatives of the output parameters. Whilethe feedback signals are typically indicative of a magnitude, thecontroller may be responsive to the signal by using a function of thevalue fedback.

When using the features described above, a versatile charger may be madethat is capable of receiving a wide range of inputs, and charging a widerange of batteries, having a number of voltages. For example, multipleoutput stages may be provided and each run off the common bus. Eachoutput stage may be controlled independently of the others, to chargeeither the same type of batteries, or different batteries, either one ata time or a plurality at a time.

Referring now to FIG. 1, a block diagram of a preferred embodiment of acharging system 100 is shown. Charger 100 includes a preregulator 102, aplurality of output circuits 104, 106, and 108, a controller 110, andfeedback lines/control inputs 112-120 that cooperate to charge batteries105, 107 and 109. While the embodiment illustrated includes three outputcircuits, other embodiments include fewer (including just one) outputcircuit, or many more output circuits. In various embodiments outputcircuits 104, 106 and 108 are fixed in place, or user interchangeable oruser-removable. Controller 110 may be located on a single board ordispersed among several boards. It may be particularly useful todisperse controller 110 among several boards, one in a housing with thepreregulator, and one with each output circuit, when the output circuitsare user-removable.

User-removable, as used herein, includes a portion of the system beinghoused in such a way as the user can remove it and replace it withrelative ease. For example, batteries on cordless power tools areuser-removable, as are batteries in automobiles. Depending upon theapplication and sophistication of the user, more or less effort by theuser is required to remove the output circuit.

The preferred embodiment provides that preregulator 102 includes a fullor half-bridge rectifier (input circuit) and a boost or buck-boostcircuit. Examples of such circuits are shown in FIGS. 2 and 3. Theiroperation is well known, and won't be described herein but a boostcircuit can increase an input voltage to a desired magnitude, and abuck-boost circuit can increase or decrease an input voltage to adesired magnitude. In various embodiments the rectifier is omitted (fordc inputs, e.g.), or combined with the boost circuit, such as shown inFIG. 4. Combined rectifier-boost, as used herein, includes a circuitsuch as FIG. 4, where the rectifier is part of the boost circuit.

Preregulator 102 receives an ac input and provides a dc bus. AC input,as used herein, includes any utility, generator, or other ac signal. Theinput can be of a different type, such as dc, in other embodiments. If adc input is used, a rectifier is not needed. The signal that causes theswitch in the boost or buck-boost converter to change states is receivedon a control input (an input for control rather than power signals). Theoperation of the preregulator results in a dc bus that is has amagnitude independent of the input magnitude, and is dc, independent ofthe input frequency. Thus, the input signal may have any frequency andmagnitude within a range of magnitudes and a range of frequencies, andpreregulator 102 will still provide the desired dc bus.

Alternative embodiments include other preregulator switched converters,such as a buck, SEPIC, or CUK converter. Converter, as used herein,includes a power circuit that receives or provides an ac or dc signal,and converts it to the other of an ac or dc signal, or to a differentfrequency or magnitude.

Controller 110 preferably controls the preregulator to be power factorcorrected to improve efficiency. The power factor correction is active,in that the controller switches the boost switch 203 to increase thepower factor. The power factor correction may be accomplished using apower factor correction circuit 204 (located in controller 110), such asan off the shelf integrated circuit that provides power factorcorrection for boost circuits.

The output of the preregulator is a dc bus at a voltage controlled bycontroller 110. The preferred embodiment provides that the converteroutput (a dc bus) be controlled to have a voltage of 950V regardless ofthe input voltage or frequency. Other bus voltages may be used.

Controller, as used herein, includes digital and analog circuitry,discrete or integrated circuitry, microprocessors, DSPs, etc., andsoftware, hardware and firmware, located on one or more boards, used tocontrol a device such as a preregulator, power circuit, or outputcircuit. Controller 110 receives power from a controller power sourcewhich may be a separate transformer based source, battery, or the dcbus.

The dc bus is maintained at a substantially constant voltage (there maybe ripple voltage or other voltage perturbations that do not adverselyimpact performance) by capacitors 206 (which may be implemented with oneor more capacitors). The invention contemplates that “dirty” power mightbe used to charge batteries. Thus, the capacitance is selected toovercome the problems caused by dirty power.

Over time, the energy provided by the generator source must be greaterthan the energy used to charge the batteries. However, for lengths oftime on the order of the period of the input power the charging energymaybe greater than the generator-provided energy. DC bus capacitors 206have a capacitance, according to the present invention, sufficient toprovide the difference between needed output power when and theavailable generator power. In the preferred embodiment, dc bus capacitor206 can store an amount of energy equal to the energy (over time)available in approximately 2.75 cycles of the input signal, or in otherwords, an amount of energy equal to approximately E=2.75(P)(T) joules,where P is the maximum output of the charger (combined for all outputcircuits) and T is the period of the generator ac signal. This overcomesthe transients that occur in the input power which are typically on theorder of a cycle T in length. In alternative embodiments of the presentinvention, capacitor 206 can store an amount of energy at least equal tothe energy (over time) available in at least 1.5 cycles of the inputsignal (or in other words, E=1.5(P)(T)), in at least 2 cycles of theinput signal (E=2(P)(T)), or in at least 2.5 cycles of the input signal(E=2.5(P)(T)).

Thus, the capacitance of capacitor 206 is C=5.5(P)(T)/(V²), where V isthe bus voltage for E=2.75(P)(T), or energy for 2.75 cycles, andC=3(P)(T)/(V²), where for 1.5 cycles, and C=4(P)(T)/(V²), for 2 cyclesand C=5(P)(T)/(V²) for 2.5 cycles.

In the preferred embodiment, the approximate values of P, T, and V are:P=1250 watts, T=16.67 milliseconds (or 20 msec for 50 Hz), and V=950volts. This results in a capacitance value for capacitor 206 of at least127 microfarads in the preferred embodiment, and capacitance values ofat least 70 microfarads, at least 92 microfarads, and at least 115microfarads, for the various equations for C described above.

Referring now to FIGS. 5 and 6, example of preferred output circuits 104and 106 are shown. The embodiment shown in FIG. 5 is a pulse-widthmodulated inverter, and the embodiment of FIG. 6 is a forward converter.The general operation of both circuits is well known. Other embodimentscontemplate frequency modulation and/or other output converters,particularly converters that switch a signal applied to a transformerprimary, and provide the output through the transformer secondary,thereby isolating the input and output.

The embodiment of FIG. 5 includes an inverter that, for example, invertsthe 950v bus through the primary of transformer 505. The secondary ofcenter-tapped transformer 505 is rectified and the dc signal is providedto charge the battery. Controller 110 modulates the pulse widths toprovide a desired output. Various embodiments include full or halfbridge topologies, or other topologies. The signal used to pulse widthor frequency modulate or otherwise control the load current and/orvoltage may be called a load control signal. The preferred outputcircuits are easily controlled to provide any output voltage. Thus, theymay be used for any type of battery within a range, so long as thebattery is identified (by the user or sensed, e.g.), and a chargingschedule is available for that battery. Also, the preferred outputcircuits may be dedicated to a single battery voltage and/or type, forexample by including control circuitry with the output circuit.

In one embodiment, a portion of controller 110 is included in thehousing that houses output circuit 104, and monitors the output currentto provide a desired charging current, in accordance with a chargingschedule provided by a charging schedule module 502 (which is part ofcontroller 110). Module, as used herein, includes software and/orhardware that cooperates to perform one or more tasks, and can includedigital commands, control circuitry, power circuitry, networkinghardware, etc. A charging schedule module is a module that provides acharging schedule.

Charging schedule module 502 includes a current module responsive tocurrent feedback and a voltage module responsive to voltage feedback inthe preferred embodiment. The current feedback may be considered part ofan inner control loop. Voltage feedback is used in an outer controlloop, to determine when the battery is nearly charged, and when thebattery voltage crosses a threshold, the charging current is greatlyreduced to a trickle charge. Other embodiments provide for monitoringthe battery temperature, and reducing charging current based ontemperature. The charging schedule can include any needed feature, suchas an initial slow charge, a discharge mode, a trickle charge, etc.Integrated circuits that provide a charging schedule are commerciallyavailable.

The housing containing output circuit 104 may also include a batterysensor 504, which is part of controller 110 and senses battery 105, andprovides a signal indicative of the battery type and/or voltage tocharging schedule module 502. Battery sensor 504 may be wired orwirelessly connected to battery 105. A wired connection allows batterysensor 504 to determine the battery voltage and/or type from the batteryterminals, or from a separate terminal on the battery which providesinformation of voltage and/or type. Battery sensor, as used herein, is asensor that determines battery type and/or voltage. The battery sensorcan be part of controller 110, or part of the output circuit.

A wireless connection is made when the battery has a wirelesstransmitter which transmits information of the battery type and voltage.One such wireless system is an RFID (radio-frequency identification)system. An RFID tag which transmits information is placed on thebattery, and sensor 504 includes an RFID receiver which receives theinformation. The information transmitted and received can be similar to“bar code” information, or it can be more or less complex. Sensor 504 isan optical bar code reader, a WIFI receiver, a magnetic strip reader orother wireless reader various embodiments. Controller 110 includes abattery selection input that receives the information from the sensor.Battery selection input, as used herein, includes any input thatreceives information, sensed or provided by the user, of battery voltageand/or type. The charging schedule module is responsive to batteryselection input, in that the charging schedule is chosen or modifiedbased on the battery type.

The battery type and/or voltage is provided on a user-selectable input,such as a panel knob, button or selector, or by instructions sent on bypda, computer, wireless controller, etc. in various embodiments to thebattery selection input on controller 110. User-selectable input, asused herein, includes any input sent from the user, either locally orremotely.

According to various embodiments each output circuit is designed for aparticular battery type and/or voltage. The output circuits may bepermanently fixed or user removable. Thus to charge a 12 volt automotivebattery the user selects the 12 volt output circuit, or automotivebattery output circuit, and connects it to the preregulator. Similarly,to charge a 24 volt battery, the user connects the 24 volt outputcircuit to the preregulator. Preferably, the connection involvessnapping a housing into place, wherein an electrical connection and astructural connection is made. For example, a portable power toolbattery is connected to the tool to make both an electrical and astructural connection.

The invention contemplates multiple output circuits connected to apreregulator at one time, as shown in FIG. 1. In such an embodiment,each output circuit includes its own control circuitry (that is part ofcontroller 110) to provide the required output (which can be sensed,set, or fixed as described above). Each output circuit receives the dcbus and inverts or converts it to its particular desired output. Thevarious output circuits may be identical or different and may providethe same or different outputs.

As described above, charging current and voltage (and batterytemperature in some embodiments) is provided to controller 110. Thatinformation, or other battery characteristics, is used, in variousembodiments, to determine whether a battery is defective (cannot beproperly charged), either because it has reached the end of itsrecharging life or perhaps because of a manufacturing defect or it hasbeen damaged. Temperature can be directly monitored or remotely sensed,such as by an infrared sensor, for example.

Controller 10 includes a defective battery sensor module 506 detects adefective battery by comparing the a battery characteristic such ascurrent and/or voltage and/or temperature to a known profile. If thecharacteristic deviates beyond a threshold, controller 110 determinesthe battery is defective. For example, some charging schedules providefor trickle charging batteries having a voltage below a threshold. Ifthe trickle charging fails to raise the voltage above a threshold, thatbattery is deemed defective. The components and or software used todetect the inability to properly charge are referred to as a defectivebattery sensor module.

When controller 110 determines a battery is defective it activates auser-noticeable output 508 such as a warning light, audible alarm, aninstant message sent remotely or an email message. The warning can besent by a wired connection or a wireless connection. User-noticeableoutput, as used herein, includes a warning indicator on a housing (suchas on the housing for the output circuit or the preregulator), or amessage sent to a telephone, pda, computer, remote indicator, etc.

Numerous modifications may be made to the present invention which stillfall within the intended scope hereof. Thus, it should be apparent thatthere has been provided in accordance with the present invention amethod and apparatus for battery charging that fully satisfies theobjectives and advantages set forth above. Although the invention hasbeen described in conjunction with specific embodiments thereof, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art. Accordingly, it is intended toembrace all such alternatives, modifications and variations that fallwithin the spirit and broad scope of the appended claims.

1. A battery charger, comprising: an input circuit configured to receivean ac input having a period of T seconds and to provide a first dcsignal; a converter configured to receive the first dc signal and toprovide a converter output across a dc bus having a peak voltage of Vvolts, and configured to receive at least one control input; an outputcircuit configured to receive the dc signal and to provide a batterycharging signal having a power of P watts; a controller, including apower factor correction circuit, configured to provide at least onecontrol signal to the converter; and a bus capacitor connected acrossthe dc bus wherein the bus capacitor has a capacitance of at least(3PT)/(V²) farads.
 2. The battery charger of claim 1 wherein thecapacitance is at least (4PT)/(V²).
 3. The battery charger of claim 1wherein the capacitance is at least (5PT)/(V²).
 4. The battery chargerof claim 1 wherein the input stage includes an input rectifierconfigured to receive the ac input signal.
 5. The battery charger ofclaim 1, further comprising a second output circuit designed for asecond battery voltage, wherein both of the output circuit and secondoutput circuit are connected at any given time.
 6. The battery chargerof claim 1, further comprising a second output circuit designed for asecond battery voltage, wherein one of the output circuit and secondoutput circuit are connected at any given time.
 7. The battery chargerof claim 5 wherein the converter is one of a buck converter, boostconverter, buck-boost convert and a combined rectifier-boost converter8. The battery charger of claim 1 wherein the output circuit includes aswitched transformer.
 9. A battery charger, comprising: an input circuitconfigured to receive an ac input having a period of T seconds and toprovide a first dc signal; a converter configured to receive the firstdc signal and to provide a converter output across a dc bus having apeak voltage of V volts, and configured to receive at least one controlinput; an output circuit configured to receive the dc signal and toprovide a battery charging signal having a power of P watts; acontroller, including a power factor correction circuit, configured toprovide at least one control signal to the converter; and a buscapacitor connected across the dc bus wherein the bus capacitor has acapacitance to store sufficient energy to maintain the available outputpower signal through the duration of mechanical transients.
 10. Abattery charger, comprising: an input circuit configured to receive anac input having a period of T seconds and to provide a first dc signal;a converter configured to receive the first dc signal and to provide aconverter output across a dc bus, and having a peak voltage of V volts,configured to receive at least one control input; a plurality ofuser-removable output circuits, each configured to receive the first dcsignal and each designed to provide a battery charging signal at adesired voltage and a desired current, wherein a chosen one of theplurality is connected at a time and the maximum power of the batterycharging signal for any of the plurality of output circuits is P watts;a controller, including a power factor correction circuit, configured toprovide at least one control signal to the converter; and a buscapacitor connected across the dc bus wherein the bus capacitor has acapacitance of at least (3PT)/(V²) farads.
 11. The battery charger ofclaim 10 wherein the capacitance is at least (4PT)/(V²).
 12. The batterycharger of claim 10 wherein the capacitance is at least (5PT)/(V²). 13.The battery charger of claim 1 wherein the input stage includes an inputrectifier configured to receive the ac input signal.
 14. The batterycharger of claim 13, further comprising a second output circuit designedfor a second battery voltage, wherein one of the output circuit andsecond output circuit are connected at any given time.
 15. The batterycharger of claim 14 wherein the converter is one of a buck converter,boost converter, buck-boost convert and a combined rectifier-boostconverter.
 16. The battery charger of claim 10 wherein the outputcircuit includes a switched transformer.
 17. A battery charger,comprising: an input circuit configured to receive an ac input having aperiod of T seconds and to provide a first dc signal; a converterconfigured to receive the first dc signal and to provide a converteroutput across a dc bus having a peak voltage of V volts, configured toreceive at least one control input; a plurality of output circuits, eachconfigured to receive the first dc signal and each designed to provide abattery charging signal at a desired voltage and a desired current,wherein each the total power provided by the plurality is of outputcircuits is P watts; a controller, including a power factor correctioncircuit, configured to provide at least one control signal to theconverter; and a bus capacitor connected across the dc bus wherein thebus capacitor has a capacitance of at least (3PT)/(V²) farads.
 18. Thebattery charger of claim 17 wherein the capacitance is at least(4PT)/(V²).
 19. The battery charger of claim 17 wherein the capacitanceis at least (5PT)/(V²).
 20. The battery charger of claim 17 wherein theinput stage includes an input rectifier configured to receive the acinput signal.
 21. The battery charger of claim 17 wherein the inputstage includes a combined rectifier-boost configured to receive the acinput signal.
 22. The battery charger of claim 20 wherein the converteris one of a buck converter, boost converter, buck-boost convert and acombined rectifier-boost converter.
 23. The battery charger of claim 20wherein the output circuit includes a switched transformer.
 24. A methodof battery charging, comprising: rectifying an ac input having a periodof T seconds to provide a first dc signal; converting the first dcsignal to provide a converter output across a dc bus at, having a peakvoltage of V volts, and configured to receive at least one controlinput; switching the dc bus to provide a battery charging signal havinga power of P watts; controlling, including power factor correcting, theconverting, and storing energy across the bus on a bus having acapacitance of at least (3PT)/(V²) farads.
 25. The method of claim 1wherein the capacitance is at least (4PT)/(V²).
 26. The method chargerof claim 1 wherein the capacitance is at least (5PT)/(V²).
 27. Themethod of claim 24, further comprising a second switching of the dc busto provide a second battery charging signal.
 28. A method of charging abattery, comprising: rectifying an ac input having a period of T secondsto provide a first dc signal; converting the first dc signal to providea converter output across a dc bus at, having a peak voltage of V volts,and configured to receive at least one control input; switching the dcbus to provide a battery charging signal having a power of P watts;controlling, including a power factor correcting, the converting, andstoring energy across the bus on a bus having a capacitance to storesufficient energy to maintain the available output power signal throughthe duration of mechanical transients.
 29. A method of charging abattery, comprising: rectifying an ac input having a period of T secondsto provide a first dc signal; converting the first dc signal to providea converter output across a dc bus at, having a peak voltage of V volts,and configured to receive at least one control input; switching the dcbus with a plurality of output circuits to provide a plurality ofbattery charging signals having a combined power of P watts;controlling, including a power factor correcting, the converting, andstoring energy across the bus on a bus having a capacitance of at least(3PT)/(V²) farads.
 30. The method of claim 29 wherein the capacitance isat least (4PT)/(V²).
 31. The method of claim 29 wherein the capacitanceis at least (5PT)/(V²).
 32. A battery charger, comprising: means forrectifying an ac input having a period of T seconds to provide a firstdc signal; means for receiving the first dc signal and for converting itand providing a converter output across a dc bus at, having a peakvoltage of V volts, and configured to receive at least one controlinput; means for switching the dc bus to provide a battery chargingsignal having a power of P watts; means for controlling, including powerfactor correcting, the converting, and means for storing energy acrossthe bus on a bus having a capacitance of at least (3PT)/(V²) farads. 33.The battery charger of claim 32 wherein the capacitance is at least(4PT)/(V²).
 34. The battery charger of claim 33 wherein the capacitanceis at least (5PT)/(V²).
 35. The battery charger of claim 32, furthercomprising a second means for switching of the dc bus to provide asecond battery charging signal.
 36. A battery charger, comprising: meansfor rectifying an ac input having a period of T seconds to provide afirst dc signal; means for converting the first dc signal to provide aconverter output across a dc bus at, having a peak voltage of V volts,and configured to receive at least one control input; means forswitching the dc bus to provide a battery charging signal having a powerof P watts; means for controlling, including a power factor correcting,the converting, and means for storing energy across the bus on a bushaving a capacitance to store sufficient energy to maintain theavailable output power signal through the duration of mechanicaltransients.
 37. A battery charger, comprising: means for rectifying anac input having a period of T seconds to provide a first dc signal;means for converting the first dc signal to provide a converter outputacross a dc bus at, having a peak voltage of V volts, and configured toreceive at least one control input; means for switching the dc bus witha plurality of output circuits to provide a plurality of batterycharging signals having a combined power of P watts; means forcontrolling, including power factor correcting, the converting, andmeans for storing energy across the bus on a bus having a capacitance ofat least (3PT)/(V²) farads.
 38. The battery charger of claim 37 whereinthe capacitance is at least (4PT)/(V²).
 39. The battery charger of claim37 wherein the capacitance is at least (5PT)/(V²).